Sepsis is a serious entity and the leading cause of death in the critically ill patients. It is characterized by a systemic inflammatory response syndrome (SIRS) and its associated multi-organ failure (MOF). The pathogenesis of sepsis associated SIRS/MOF is still poorly understood and therapeutic/diagnostic options remain limited. One of the remaining questions for the development of SIRS/MOF is how the focal infections are exaggerated to systemic inflammation. Based on our published and preliminary studies, we believe that exosomal-shuttle miRNAs play crucial roles in transporting inflammatory signals to the distant target cells and organs. miR-15a and miR-16 are clustered closely at the same chromosome position, thus, carrying similar cellular functions. We believe that miR-15a/16 mediate macrophage over-activation and transport the inflammatory signals to distant targets, via the macrophage released exosomes (extracellular vesicles). The generation and encapsulation of miR-15a/16 into the exosomes require PTRF, a novel lipid raft protein shuttling between plasma membrane and nuclei. Consistently, our published studies have demonstrated that deletion of PTRF protected mice from SIRS/MOF/death after CLP and deceased macrophage derived NO/ROS. In this proposal, we hypothesize that exosomal (EV)-shuttle miR-15a/16 plays crucial roles in sepsis induced SIRS and its associated MOF. Our studies potentially provide novel therapeutic and diagnostic targets for SIRS/MOF after sepsis, which is highly relevant to clinical practice. Macrophages, the first arm of defense in the immune system, play crucial roles in the transmission and amplification of inflammatory signals. Therefore, we use macrophages as the cellular models. Cecal ligation and puncture (CLP) is used as an in vivo sepsis model. We will test our hypotheses in the following specific aims: Aim I: To determine the generation, secretion and regulation of miR-15a/16 in macrophages in vitro. Aim II: To determine the cellular functions of miR-15a/16 in macrophages in vitro. Aim III: To determine the functional roles of exosomal (EV)- shuttle miR-15a/16 in sepsis in vivo.